The following abbreviations are herewith expanded, at least some of which are referred to within the following description of the state-of-the-art and the present invention.    AD Alien Detection    CO Central Office    GPON Gigabit PON    OLT Optical Line Terminal    ONT Optical Network Terminal    ONU Optical Network Unit    PON Passive Optical Network
A PON (passive optical network) may be used as an access network, connecting individual subscribers or groups of subscribers to a core telecommunications network. A typical PON includes, among other components, an OLT (optical line terminal) in a CO (central office) and a number of ONUs (optical network units) at subscriber premises (or some intermediate location). Many residential houses, for example, have an ONU that communicates with an OLT over a FTTH (fiber to the home) PON access network. The network may make available to the subscriber services such as Internet access, telephone, and television.
As may be apparent, an OLT in the CO is a relatively permanent part of the PON; at least it typically remains in place for some time serving the various ONUs connected to it. Each ONU, however, is generally in place only so long as the subscriber subscribes to the services provided via the PON. Even where subscribers buy the ONU equipment, it will typically become inoperative as part of the network when then subscription is terminated. New subscribers, on the other hand, acquire or are provided with ONUs for use with the PON. An ONU may in some cases move from one location to another, but cannot be used there unless it is compatible with the PON, which frequently it will not be. In any case, when a properly configured ONU is in place and a subscription begins, the ONU may be linked (registered) with the OLT and service provided.
In some environments, PON providers supply all necessary equipment to the subscriber, including the ONU; the provider may even install the ONU and ensure it is working. In other environments, subscribers may purchase and install their own equipment. In the latter case, it is possible in some cases, for example open access environment with multiple operators, an ONU may be connected to the wrong PON. This may occur, for instance, in a multi-subscriber dwelling where many subscribers may be connected to a number of different providers. Additionally, other optical systems, such as Point-to-Point may also share the same fiber infrastructure and also act to disrupt the PON system on the same fiber. Generally, an ONU connected to the wrong operator's PON or fiber will not be able to link with the OLT and no service will be provided to it.
Unfortunately, this “alien ONU” (or other alien device) can still disrupt PON operations. While upstream transmissions from the alien ONU typically do not detectably affect performance characteristics during regular PON operation, they are frequently sufficient to frustrate ranging procedures. When this occurs, legitimate PON ONUs are frequently unable to link with the OLT, either initially or when being brought back on line. These circumstances, however, make the presence of alien ONUs very difficult to detect.
Accordingly, there has been and still is a need to address the aforementioned shortcomings and other shortcomings associated with alien ONUs. These needs and other needs are satisfied by the present invention.